The present disclosure relates generally to natural sweeteners. More particularly, the present disclosure relates to a non-caloric sweetener and methods for synthesizing the non-caloric sweetener.
Steviol glycosides are natural products isolated from Stevia rebaudiana leaves. Steviol glycosides are widely used as high intensity, low-calorie sweeteners and are significantly sweeter than sucrose. Naturally occurring steviol glycosides share the same basic steviol structure, but differ in the content of carbohydrate residues (e.g., glucose, rhamnose and xylose residues) at the C13 and C19 positions. Steviol glycosides with known structures include, steviol, stevioside, rebaudioside A, rebaudioside B, rebaudioside C, rebaudioside D, rebaudioside E, rebaudioside F and dulcoside A (see e.g., Table 1).
TABLE 1Steviol glycosides.MolecularMolecularNameStructureFormulaWeightSteviolC20H30O3 318 SteviosideC38H60O18 804 Rebaudioside AC44H70O23 966 Rebaudioside- BC38H60O18 804 Rebaudioside CC44H70O22 950 Rebaudioside DC50H80O281128 Rebaudioside EC44H70O23 966 Rebaudioside FC43H68O22 936 Rebaudioside D3C50H80O281128 Dulcoside AC38H60O17 788
On a dry weight basis, stevioside, rebaudioside A, rebaudioside C, and dulcoside A, account for 9.1, 3.8, 0.6, and 0.3% of the total weight of the steviol glycosides in the leaves, respectively, while the other steviol glucosides are present in much lower amounts. Extracts from the Stevia rebaudiana plant are commercially available, which typically contain stevioside and rebaudioside A as primary compounds. The other steviol glycosides typically are present in the stevia extract as minor components. For example, the amount of rebaudioside A in commercial preparations can vary from about 20% to more than 90% of the total steviol glycoside content, while the amount of rebaudioside B can be about 1-2%, the amount of rebaudioside C can be about 7-15%, and the amount of rebaudioside D can be about 2% of the total steviol glycosides.
Steviol glycosides differ from each other not only by molecular structure, but also by their taste properties. For example, different steviol glycosides have different degrees of sweetness and after-taste. Stevioside, for example, is 100-150 times sweeter than sucrose, but has a bitter after-taste. Rebaudioside A and rebaudioside E, for example, are 250-450 times sweeter than sucrose and have less of an after-taste than stevioside. Rebaudioside C is between 40-60 times sweeter than sucrose. Dulcoside A is about 30 times sweeter than sucrose.
The majority of steviol glycosides are formed by several glycosylation reactions of steviol, which are typically catalyzed by the UDP-glycosyltransferases (UGTs) using uridine 5′-diphosphoglucose (UDP-glucose) as a donor of the sugar moiety. UGTs in plants make up a very diverse group of enzymes that transfer a glucose residue from UDP-glucose to steviol. For example, glycosylation of the C-3′ of the C-13-O-glucose of stevioside yields rebaudioside A; and glycosylation of the C-2′ of the 19-O-glucose of the stevioside yields rebaudioside E. Further glycosylation of rebaudioside A (at C-19-O-glucose) or rebaudioside E (at C-13-O-glucose) produces rebaudioside D. (FIG. 1).
Alternative sweeteners are receiving increasing attention due to awareness of many diseases in conjunction with the consumption of high-sugar foods and beverages. Although artificial sweeteners are available, many artificial sweeteners such as dulcin, sodium cyclamate and saccharin have been banned or restricted by some countries due to concerns over their safety. Therefore, non-caloric sweeteners of natural origin are becoming increasingly popular. One of the main obstacles for the widespread use of stevia sweeteners are their undesirable taste attributes. Accordingly, there exists a need to develop alternative sweeteners and methods for their production to provide the best combination of sweetness potency and flavor profile.